Sidewalk/Street Design

"Streets and their sidewalks, the main public places of a city, are its most vital organs."

Credit: greatstreets.org

The quote above from Jane Jacobs describes the critical role streets and sidewalks play in our communities. Our streets and sidewalks are the centerpieces around which great places can be developed.

In addition to being the primary infrastructure of our transportation network, streets and sidewalks are the major identifier of a community and have a direct impact on the overall character and feel of a place. Consider the street shown in the image at right.

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While a variety of characteristics help shape this great street, the type, texture, and color of the pavement play a significant role. The character of the thoroughfare would change dramatically with standard, generic pavement type and sidewalk. In the next image, the pavement striping, color, width, and streetscape amenities found in the corridor largely contribute to the area's appeal. The bike lane's contrasting color increases driver awareness and adds to the thoroughfare's aesthetic character.

Street Width:

In a great street, space allocation for pavement must consider vehicular capacityneeds, bicycle lane or shoulder provisions, and the design speed for the facility. Capacity considerations will generally govern how many lanes are required for vehicular traffic, while the facility's target speed and design vehicle influence how wide each lane should be. The presence and type of median treatments and the need to provide bicycle lanes will also influence overall thoroughfare width, as will the existing right-of-way. Thoroughfare width will also reflect the target level of service . If the target performance for a given thoroughfare is set at LOS B, for example, the number of lanes needed to accommodate through-traffic and turning movements will be much higher than if the target is set at LOS E. In many cases, setting higher level-of-service targets will result in a much wider thoroughfare. Setting lower targets (i.e. tolerating more congestion on a given facility) can help limit thoroughfare width and/or free up space for non-vehicular, multi-modal treatments.

Vehicular mobility is one of many considerations in thoroughfare design. It is often appropriate to design narrower thoroughfares with lower vehicular capacity to accommodate the needs of pedestrians, bicycles and transit. Thoroughfare planners should work with local agencies, businesses, and residents when determining specific requirements for each place. See the capacity section of this manual for more information.

Vehicular Travel Lane Width:

Based on the perception that wider lanes are safer,the St. Louis region has historically used 12-foot travel lanes for many thoroughfares. Recent studies show that at speeds of 35 mph or less, there is very little difference in substantivesafetyperformance for lane widths of ten, eleven, and twelve feet. Narrower travel lanes can also have a traffic calming effect on a thoroughfare by causing vehicles to drive slower. Conversely, wider lanes often encourage motorists to travel above the facility's target speed. If narrower lanes are chosen, it is important to carefully design the pavement (whether flexible or rigid) to maximize pavement life cycle. Pavement selection for narrower lanes should focus on durability to offset the effects of a confined wheel track space, which can produce early fatigue.

Design narrow lanes. Because slower speeds are desirable, lane widths under twelve feet are recommended, with 10' as the minimum. Tables 6.2 and 6.3 of the ITE publication Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities provides excellent design parameters for arterial and collector streets. These tables recommend a lane width of 10-11' for the majority of place types, including those discussed in this guide. Chapter 9 of the ITE publication also provides useful guidance on lane width.

A bicycle lane should be provided along thoroughfares which are designated bicycle routes, whenever feasible. When bicycle lanes are not possible due to existing right-of-way constraints, a wider outside travel lane should be considered. A shared bicycle-parking lane may be provided along thoroughfares needing bicycle lanes and on-street parking. General width recommendations are as follows:

Dedicated bicycle lane: minimum width is four (4) feet with an open shoulder or five (5) feet when bordered by a curb, guardrail, or other roadside barrier

Wider outside travel lane: minimum width is 12' (at widths under 12' cyclists should take the full lane for their safety), and maximum width is 14' (lanes wider than 14' feel and may be treated like two lanes to motorists)

A number of (often conflicting) forces influence the appropriate width for sidewalks along a given corridor, including the current or anticipated pedestrian presence, abutting land uses, and utility requirements. See Chapter 3.2.3 of AASHTO's Guide for the Planning, Design, and Operation of Pedestrian Facilities for more guidelines on establishing a suitable sidewalk width in various types of corridors.

Although the minimum clear width required for sidewalks is four (4) feet, most of the place types discussed in this guide, especially those with a significant pedestrian presence should elect to include significantly wider sidewalks.

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Even in areas of low pedestrian presence, a minimum of five (5) feet is desirable where separated from the curb by a tree lawn, or six (6) feet where adjacent to a curb. See the pedestrianssection of this manual for place-type-specific recommendations on sidewalk width.

The table at right, from Oregon Metro's "Creating Livable Streets," also provides excellent guidelines for minimum width requirements as they relate to other elements of the streetscape.

Aesthetic Treatments:

Choosing the appropriate width for streets and sidewalks, although important, is just one of many considerations in creating attractive, livable streets and places. Various design treatments, such as colored or textured pavement, brick pavers, cobblestones, and granite curbs can be used to visually enhance the streetscape, as shown in the images below.

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Although these treatments typically cost more to construct, in downtown areas they can help create identity and create a much safer and attractive place, which has clear economic benefits.

Some treatments, such as the cobblestone midblock pedestrian crossing shown below, can also have traffic calming effects at key locations.

Credit: CH2M HILL

Credit: CH2M HILL

Linking the design of these treatments with the architectural character of surrounding land uses creates an even more attractive and cohesive corridor.

Treatments such as raised brick pavers or cobblestones should not be used in bicycle lanes, as they can be hazardous or uncomfortable for bicyclists to navigate.

Credit: CH2M HILL

Likewise, decorative sidewalk treatments should not interfere with ADA compliance. The image at right is an example of an attractive, ADA-compliant treatment.

Inserting artistic design treatments intermittently, rather than along the entire sidewalk (as shown in the image below, at left), is a cost-effective way to enhance the streetscape.

When linked with the surrounding land uses, colored sidewalks (as shown in the image below, at right) can be a great way to revamp a corridor.

This treatment is generally less expensive than pavers or other special material applications.